CYTOLOGICAL STUDIES OF CENTRIFUGED EGGS 645 
supernumerary sperm are prevented from entering, does not take 
place so quickly when sperm enter at other regions than the normal 
one. If we think of the spermatozoa as boring into the sur- 
face of the egg, we must suppose in the present case that they con- 
tinue to do so until the occluding reaction has occurred. If on the 
other hand we think of the entrance of the spermatozoon as involv- 
ing a responsive reaction on the part of the cytoplasm, we must sup- 
pose in the present case that this reaction persists until the first 
spermatozoon having reached the region of the blastodisc, the 
occluding reaction sets in and prevents further entrance. Possi- 
bly the result may be more simply explained on the ground that 
the peripheral protoplasm is so thin that the reaction is insufficient 
to occlude for some time the entering sperm. 
If the egg is first fertilized and then centrifuged, the microblas- 
todiscs do not appear. This shows that the occluding reaction 
is effective, when normally carried out, not only for the region 
of normal entrance, but for all the rest of the protoplasm as well. 
The transportation of the sperm at times over an extensive 
region of the egg in a thin layer of protoplasm is one of the most 
remarkable phenomena that I have to record. Until we know 
more about the cause of the movement of the sperm nucleus it is 
idle to speculate on this case; but the fact of its transportation 
over a long distance in an attenuated layerof protoplasm is worthy 
of remark. 
The cleavage of these eggs offers many anomalies. In a few 
cases the blastodisc divides normally into two equal cells. These, 
and only these eggs, produce normal embryos, as I have deter- 
mined by isolating them. Most of the eggs break up irregularly 
into several cells (fig. G, H, I) resembling in every respect the 
abnormal segmentation observed in eggs with delayed fertiliza- 
tion, and, like the latter, produce abnormal blastoderms. 
Some of the eggs show a more peculiar relation. The main 
blastoderm divides regularly into two cells, while at one edge 
a small independent microblastodisc also divides. These two 
may later intimately fuse. From such eggs some of the most 
interesting types of embryos that I have seen may be supposed 
to have come. These embryos are defective on one side (figs. 
THK JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 9, NO. 3. 
